1. Field of the Invention
The present invention generally relates to a vibration motor suitable for a communication apparatus notifying a user of incoming calls and, more particularly, to a vibration motor having an improved brush of a stator contacting a commutator of a rotor in order to maintain line contact between the brush and the commutator and to stabilize the vibration motor.
2. Background Art
One of essential functions in a communication apparatus is a notifying function to notify a user of incoming calls. Both a vibration mode for vibrating the communication apparatus and a sound mode for generating melody sound or bell sound have been used for the notifying function in the communication apparatus.
In accordance with the user""s preference of the notifying function, one of the vibration mode and the sound mode is activated to notify the user of the incoming calls
The vibration mode has been used for preventing noise generation and avoiding offensive influences exerted on a group of people by the sound generated in the sound mode.
Generally, in the sound mode, one of a variety of melody sound stored in the communication apparatus is generated from a speaker mounted in the communication apparatus, and the user may be notified by the one of the melody sound generated from the speaker. In the vibration mode, vibration generated from a vibration motor mounted in the communication apparatus propagates to an outer casing of the communication apparatus.
A conventional vibration mode is performed by a vibration motor mounted inside the communication apparatus. The vibration motor having a coin type or a pan cake type in shape and having a diameter greater than a height of the vibration motor is shown in FIGS. 1 and 2.
The vibration motor includes a cover plate 100, a bore 100a formed on a central portion of cover plate 100 and raised from cover plate 100 by a predetermined height, a stationary shaft 140 having a low portion forcibly inserted into bore 100a of cover plate 100, and a first printed circuit board (PCB) 110 disposed on cover plate 100 and coupled to an external power source.
A ring-shaped magnet 130 inserted around shaft 140 is disposed on first PCB 110 and includes N and S magnetic field poles alternatively arranged around shaft 140 to form a ring shape.
A pair of brushes 120 is disposed within a central hole formed on ring-shaped magnet 130 and includes a first end connected to first PCB and a second end upwardly extended and raised from the first end. Brushes 120 are spaced-apart from each other.
A cylindrical case 150 having a circular plate, a circumferential cylindrical side extended from the circular plate, and an opening defined by the circumferential cylindrical side and facing cover plate 100 is coupled to circumferential peripheral side of cover plate 100 to cover an upper side of cover plate 100. A support hole 150a is formed on a central portion of the circular plate of case 150. A low portion of stationary shaft 140 is supported by bore 100a while an upper portion of shaft 140 is supported by supporting hole 150a of cylindrical case 150 when cylindrical case 150 is coupled to cover plate 100.
A stator of the vibration motor includes cover plate 100, shaft 140 supported by both cover plate 100 and cylindrical case 150, first PCB 110 disposed on cover plate 100, ring-shaped magnet 130, the pair of brushes 120, and cylindrical case 150. An eccentric rotor 200 of the vibration motor disposed between ring-shaped magnet 130 and the circular plate of case 150 includes a bearing b rotatably inserted around shaft 140, a second PCB coupled bearing b, a plurality of coils 240, and a commutator 220.
Second PCB 210 is supported by bearing b and rotates about shaft 140. A plurality of commutator 220 is integrally formed on a bottom surface of second PCB facing first PCB. A segment of commutator 220 comes into contact with the second end of brushes 120 coupled to first PCB 110. The external electric power is transmitted to coils 240 through first PCB 110, brushes 120, and commutator 220.
Second PCB 210 includes an insulator 250 filled between coils of rotor 200. Insulator 250 is integrally formed on second PCB 210 with commutator 220 and coils 240 by insert molding. A weight 230 is disposed between two adjacent coils 240 in order to increase the amount of eccentric force.
When the external electric power is fed to first PCB 110, the electric power is supplied to coils 240 through the first ends of the pair of brushes 120 coupled to first PCB 110, commutator 220 being contact with the second ends of brushes 120. Therefore, the interaction between a first magnetic field generated by coils 240 and a second magnetic field generated from ring-shaped magnet 130 rotates rotor 200 about shaft 140.
Since rotor 200 is eccentrically supported by shaft 140, the eccentric rotation of rotor 200 propagates to cover plate 100 and case 150 through shaft 140 and causes case 150 to vibrate. This vibration of case 150 is used for silently notifying a user of incoming calls.
However, brushes 120 in the conventional vibration motor come into unstable contact with commutator 220. Therefore, the unstable contact between brushes 120 and commutator 220 causes electric spark and noise which not only shorten the life time of brushes 120 and commutator 220 of the vibration motor but deteriorate the notifying function of the communication apparatus.
Brushes 120 having an arcuate shape are arranged around opposite sides of shaft 140 as shown in FIGS. 3 and 4. Each of brushes 120 includes a first bending portion 121 bent in a vertical direction from a predetermined portion of the first end, a second bending portion 122 upwardly extended from first bending portion 121 and being slant with respect to both first bending portion 121 and commutator 220, a curved portion 123 extended from second bending portion 122 and being contact with commutator 220.
Curved portion 123 of brushes 120 is bent in both a radial direction a and an arcuate direction while being slant with respect to commutator 220. Since curved portion 123 is bent in lengthwise about the contact between commutator 220 and brushes 120, brushes 120 shows differences h1, h2 between bending curvatures of an inside portion and an outside portion of brushes around the contact. This difference cause curved portion 123 of brushes 120 does not come to uniform contact with commutator. The amount of the contact varies along the width w of brushes 120 between the inside portion and the outside portion of brushes 120 as a gap P varies along the width w of curved bending portion 123 of brushes where curved bending portion 123 is contact with commutator 220.
Therefore, brushes 120 come into partial point contact with commutator 220 because of the differences h1, h2 formed along the width w of curved portion 123 of brushes 120. Non-uniform scratches are formed on commutator 220 as shown in FIG. 6. The non-uniform scratches affect the contact between commutator 220 and brushes 120.
The contact between brushes 120 and commutator 220 becomes irregular because brushes 120 does not come to uniform contact with commutator 220 but come to point contact with commutator.
A lowered current wave lower than a reference current wave d is shown in FIG. 7 in a predetermined period of operation time after the vibration motor operates. As the non-uniform contact between brushes 120 and commutator 220 gradually increases, instantaneous sparks are frequently generated between brushes 120 and commutator 220 due to the increment of current density and instant current density. The abrasion of brushes 120 deteriorates reliability of the vibration motor.
It is an object of the present invention to provide an improved vibration motor able to prevent non-uniform abrasion of a brush of a stator contacting a commutator of a rotor.
It is another object to provide an improved vibration motor able to maintain a brush of a stator to be line-contact with a commutator of a rotor.
It is still another object to provide an improved vibration motor able to allow a brush of a stator to be uniform contact in a radial direction with a commutator of a rotor.
It is yet another object to provide a vibration motor able to improve the reliability of a stator and a rotor.
It is a further object to provide a vibration motor having an improved brush of a stator in shape.
It is also an object to provide a vibration motor able to prevent a spark phenomenon caused by the non-uniform contact between a brush of a stator and a commutator of a rotor.
These and other objects may be achieved by providing a vibration motor including a cover plate, a case coupled to the cover plate and providing an internal space, a shaft having a low portion forcibly inserted into a bore which is formed on a central portion of the cover plate and raised from the cover plate, a first printed circuit board (PCB) disposed on the cover plate and coupled to an external power source, a magnet disposed on the first PCB and around the bore and including N and S magnetic field poles alternatively arranged around the shaft, a second PCB rotatably supported by a bearing inserted around the shaft and integrally provided with a plurality of commutators on a bottom surface of the second PCB facing the first PCB, an insulator fixing coils on the second PCB, and a pair of brushes disposed within a central hole formed on the magnet and including a first end connected to the first PCB and a second end upwardly extended from the first end and raised from both the first end and the magnet, the second end including a curved bending portion being line contact with the commutator.
The pair of brushes includes a first extension disposed on the first PCB to be coupled to a terminal portion of the first PCB and extended along a straight line parallel to a central line or tangent to an arcuate line formed around the bore, a second extension upwardly extended from the first extension at a first bending line having a first angle with the straight line or the central line and bent in a longitudinal plane, and a curved bending portion extended from the second extension at a second bending line and being line contact with the commutator and bent lengthwise in the arcuate direction around the shaft while the line contact is in a radial direction of shaft and parallel to commutator or the second PCB.
Another embodiment of the vibration motor includes a cover plate, a case coupled to the cover plate and providing an internal space, a shaft having a low portion forcibly inserted into a bore which is formed on a central portion of the cover plate and raised from the cover plate, a first printed circuit board (PCB) disposed on the cover plate and coupled to an external power source, a magnet disposed on the first PCB and around the bore and including N and S magnetic field poles alternatively arranged around the shaft, a second PCB rotatably supported by a bearing about the shaft and integrally provided with a plurality of commutators on a bottom surface of the second PCB facing the first PCB, an insulator fixing coils on the second PCB, and a pair of brushes disposed within a central hole formed on the magnet and including a first end connected to the first PCB and a second end upwardly extended from the first end and raised from both the first end and the magnet, the second end including a curved bending portion being line contact with the commutator and a intermediate portion formed between the first end and the second end and being parallel to one of the first PCB and the second PCB.
The brushes includes a first extension, a second extension upwardly extended from the first extension, the intermediate portion being parallel to the commutator, and the curved bending portion extended from the intermediate portion to be line contact with the commutator.